(a) Field of the Invention
The present invention relates to a battery charging system and method for a hybrid vehicle and the hybrid vehicle using the same. More particularly, the present invention relates to a battery charging system and method and a vehicle using the same that use a main drive motor to charge the battery.
(b) Description of the Related Art
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors powered by a battery. However, alternative forms of hybrid vehicles do exist, Hybrid Fuel cell vehicles. Hybrid vehicles have become increasingly popular over the last couple of years due to their high fuel efficiency and low impact on the environment.
Generally, hybrid vehicles can be split into two distinct species, parallel type hybrids and series type hybrid. In a parallel hybrid one or more electric motors and an internal combustion engine are installed so that they can both individually or together power the vehicle. However in a series hybrid the vehicle is driven by the electric motor with no mechanical connection to the engine. Instead the engine is configured to run a generator when the battery pack energy supplied to the motor isn't or is being charged.
Additionally, hybrid vehicles can also be compound type hybrid in which power paths from the engine to the wheels that can be either mechanical or electrical. The main principle behind this system is the decoupling of the power supplied from the engine (or other primary source, such as a fuel cell) from the power demanded by the driver. Thus, these types of hybrid vehicles mix the elements of a parallel hybrid and a series hybrid vehicle.
Most hybrid electric vehicles include a low voltage battery in which low DC voltage (e.g., 24V) is stored in addition to high voltage battery (e.g., 500V). Lighting devices such as the head lamps or a brake lights, air conditioning devices (e.g., the compressor or condenser, sound systems, or control devices such as various controllers or a vacuum pump for applying the brakes are operated by power from the low voltage battery.
Since a portion of the energy powering the vehicle in a hybrid comes from the batteries, charging the batteries is very important in hybrid electric vehicles. Charging method differs according to operating modes in for example a parallel hybrid. In the conventional design, small amounts of power can be restored in the battery via a hybrid starter generator (HSG), but the battery cannot be charged via the main (drive) motor when the vehicle is stopped. On the contrary, the battery can be charged via the main motor only when the vehicle is running or in motion. Thus, since the battery may not receive a sufficient restoration of power from the HSG when the vehicle is stopped, the battery may become completely drained. When the battery becomes drained beyond a certain threshold, the motor cannot be sufficiently used when the vehicle begins to move. Therefore, drivability of the hybrid vehicle and fuel economy may be deteriorated significantly as a result.
When the vehicle is stopped on a road having a slope less than or equal to a predetermined slope (for example, 4%), an under-drive (UD) clutch in a transmission is slips once the battery becomes charged in a neutral position to provide power to a motor to operate the vehicle. When the vehicle, however, is stopped on a road having a slope greater than the predetermined slope, slip energy is very excessive and the battery cannot be charged by using the motor in a neutral position. Therefore, charging methods for the hybrid vehicle should be studied and improved so as to charge the battery in various environments efficiently.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.